Habitat use and its implications to functional morphology: niche partitioning and the evolution of locomotory morphology in Lake Tanganyikan cichlids (Perciformes: Cichlidae)

Historical biogeography and the evolution of habitat preference in the North American camel spider family, Eremobatidae (Arachnida:Solifugae)

Abiotic variables can influence species distributions, often restricting taxa to an acquired climatic signature or conversely, related species are conserved in the same ecological space over millions of years. An investigation into how abiotic change has shaped geographic distributions of taxa may be key to understanding diversification of lineages, and in the absence of reliable morphological characteristics, such information may support taxonomic units at multiple scales. Here, we examine the historical biogeography and patterns of habitat preference within the North American solifuge family, Eremobatidae. A previous study demonstrated that a major taxonomic revision of Eremobatidae is warranted, however recent studies demonstrate high levels of morphological convergence within the group, thus a re-classification of generic boundaries using additional information must be prioritized before we can formally begin solid revisionary efforts. In this study, we aimed to reconstruct a well-resolved phylogenetic hypothesis of Eremobatidae by filtering UCE loci based on informativeness, by mitigating the effect of cogenic UCE on phylogenetic estimation, and by supplementing our curated UCE loci with mitochondrial information. Using our preferred topology, in conjunction with published estimated divergence dates for Eremobatidae, we inferred a time-calibrated phylogenetic hypothesis to inform the historical biogeography and patterns of habitat preference. The two major habitat types that were observed for Eremobatidae were warm deserts for early diverging taxa and a subsequent evolution to cold deserts and Mediterranean California ecoregions for later diverging taxa. Eremobatid niche space, determined by temperature and precipitation, has been conserved for at least 25 million years in North America, supporting a warm desert origin, and thus supporting high species richness in the Sonoran and Mexican Plateau. Overall, our study provides support for new generic level designations within Eremobatidae.

Historical Field Records Reveal Habitat as an Ecological Correlate of Locomotor Phenotypic Diversity in the Radiation of Neotropical Geophagini Fishes

AbstractPhenotypic macroevolutionary studies provide insight into how ecological processes shape biodiversity. However, the complexity of phenotype-ecology relationships underscores the importance of also validating phenotype-based ecological inference with direct evidence of resource use. Unfortunately, macroevolutionary-scale ecological studies are often hindered by the challenges of acquiring taxonomically and spatially representative ecological data for large and widely distributed clades. The South American cichlid fish tribe Geophagini represents a continentally distributed radiation whose early locomotor morphological divergence suggests habitat as one ecological correlate of diversification, but an association between locomotor traits and habitat preference has not been corroborated. Field notes accumulated over decades of collecting across South America provide firsthand environmental records that can be mined for habitat data in support of macroevolutionary ecological research. In this study, we applied a newly developed method to transform descriptive field note information into quantitative habitat data and used it to assess habitat preference and its relationship to locomotor morphology in Geophagini. Field note-derived data shed light on geophagine habitat use patterns and reinforced habitat as an ecological correlate of locomotor morphological diversity. Our work emphasizes the rich data potential of museum collections, including often-overlooked material such as field notes, for evolutionary and ecological research.

Movement patterns and habitat use for the sympatric species: Gambelia wislizenii and Aspidoscelis tigris

Movement is an important characteristic of an animal's ecology, reflecting the perception of and response to environmental conditions. To effectively search for food, movement patterns likely depend on habitat characteristics and the sensory systems used to find prey. We examined movements associated with foraging for two sympatric species of lizards inhabiting the Great Basin Desert of southeastern Oregon. The two species have largely overlapping diets but find prey via different sensory cues, which link to their differing foraging strategies-the long-nosed leopard lizard, Gambelia wislizenii, is a visually-oriented predator, while the western whiptail, Aspidoscelis tigris, relies more heavily on chemosensory cues to find prey. Using detailed focal observations, we characterized the habitat use and movement paths of each species. We placed markers at the location of focal animals every minute for the duration of each 30-min observation. Afterward, we recorded whether each location was in the open or in vegetation, as well as the movement metrics of step length, path length, net displacement, straightness index, and turn angle, and then made statistical comparisons between the two species. The visual forager spent more time in open areas, moved less frequently over shorter distances, and differed in patterns of plant use compared to the chemosensory forager. Path characteristics of step length and turn angle differed between species. The visual predator moved in a way that was consistent with the notion that they require a clear visual path to stalk prey whereas the movement of the chemosensory predator increased their chances of detecting prey by venturing further into vegetation. Sympatric species can partition limited resources through differences in search behavior and habitat use.

Comparative analysis of cranial morphology in Middle-American heroine cichlids (Actinopterygii: Cichliformes)

Heroine cichlids are characterized by high morphological diversity, mainly in structures related to the capture and processing of food. The existence of ecomorphological groups has been proposed based on feeding behavior, where it is common for some phylogenetically unrelated species to show evolutionary convergence. Using geometric morphometrics and comparative phylogenetic methods, the variation in cranial morphology was evaluated for 17 species of heroine cichlids representing 5 ecomorphs. Cranial ecomorphs were recovered and significant differences were determined. Morphological variation of the ecomorphs was mainly explained by two axes: (1) the position of the mouth determined by the shape of the bones of the oral jaw and (2) the height of the head, defined by the size and position of the supraoccipital crest and the distance to the interopercle-subopercle junction. Cranial variation among species was related to phylogeny. To better understand the evolution of cranial morphology, it is necessary to evaluate the morphofunctional relationship of other anatomical structures related to feeding, as well as to increase the number of study species in each ecomorph by including other lineages.

Comparative scale morphology in the adaptive radiation of cichlid fishes (Perciformes: Cichlidae) from Lake Tanganyika

The morphology of fish scales has been investigated for > 200 years, but research on evolutionary patterns of scale morphology is scarce. Here, we study scale morphology and its evolution in the adaptive radiation of cichlid fishes from Lake Tanganyika, which are known for their exceptional diversity in habitat use, feeding ecology and morphology. Based on a geometric morphometric approach on eight scales per specimen (covering different body regions), we quantify scale types and morphology across nearly all ~240 species of the cichlid adaptive radiation in Lake Tanganyika. We first show that scale type, shape and ctenii coverage vary along the body, which is probably attributable to adaptations to different functional demands on the respective scales. Our comparative analyses reveal that flank scale size is tightly linked to phylogeny, whereas scale shape and ctenii coverage can be explained only in part by phylogenetic history and/or our proxy for ecology (stable isotopes and body shape), suggesting an additional adaptive component. We also show that our measured scale characteristics can help to assign an individual scale to a taxonomic group or ecotype. Thus, our data may serve as a valuable resource for taxonomic studies and to interpret fossil finds.

Trophic divergence of Lake Kivu cichlid fishes along a pelagic versus littoral habitat axis

Local adaptation to the littoral and pelagic zones in two cichlid haplochromine fish species from Lake Kivu was investigated using morphometrics. Cranial variation and inferred jaw mechanics in both sexes of the two species across the two habitat types were quantified and compared. Comparisons of littoral versus pelagic populations revealed habitat-specific differences in the shape of the feeding apparatus. Also, kinematic transmission of the anterior jaw four-bar linkage that promotes greater jaw protrusion was higher in the pelagic zone than in the littoral zone for both species. Inferred bite force was likewise higher in pelagic zone fish. There were also sex-specific differences in craniofacial morphology as males exhibited longer heads than females in both habitats. As has been described for other cichlids in the East African Great Lakes, local adaptation to trophic resources in the littoral and pelagic habitats characterizes these two Lake Kivu cichlids. Similar studies involving other types of the Lake Kivu fishes are recommended to test the evidence of the observed trophic patterns and their genetic basis of divergences.

Work that body: fin and body movements determine herbivore feeding performance within the natural reef environment

Herbivorous fishes form a keystone component of reef ecosystems, yet the functional mechanisms underlying their feeding performance are poorly understood. In water, gravity is counter-balanced by buoyancy, hence fish are recoiled backwards after every bite they take from the substrate. To overcome this recoil and maintain contact with the algae covered substrate, fish need to generate thrust while feeding. However, the locomotory performance of reef herbivores in the context of feeding has hitherto been ignored. We used a three-dimensional high-speed video system to track mouth and body kinematics during in situ feeding strikes of fishes in the genus Zebrasoma, while synchronously recording the forces exerted on the substrate. These herbivores committed stereotypic and coordinated body and fin movements when feeding off the substrate and these movements determined algal biomass removed. Specifically, the speed of rapidly backing away from the substrate was associated with the magnitude of the pull force and the biomass of algae removed from the substrate per feeding bout. Our new framework for measuring biting performance in situ demonstrates that coordinated movements of the body and fins play a crucial role in herbivore foraging performance and may explain major axes of body and fin shape diversification across reef herbivore guilds.

Newly discovered cichlid fish biodiversity threatened by hybridization with non-native species

Invasive freshwater fishes are known to readily hybridize with indigenous congeneric species, driving loss of unique and irreplaceable genetic resources. Here we reveal that newly discovered (2013-2016) evolutionarily significant populations of Korogwe tilapia (Oreochromis korogwe) from southern Tanzania are threatened by hybridization with the larger invasive Nile tilapia (Oreochromis niloticus). We use a combination of morphology, microsatellite allele frequencies and whole genome sequences to show that O. korogwe from southern lakes (Nambawala, Rutamba and Mitupa) are distinct from geographically disjunct populations in northern Tanzania (Zigi River and Mlingano Dam). We also provide genetic evidence of O. korogwe × niloticus hybrids in three southern lakes and demonstrate heterogeneity in the extent of admixture across the genome. Finally, using the least admixed genomic regions we estimate that the northern and southern O. korogwe populations most plausibly diverged ~140,000 years ago, suggesting that the geographical separation of the northern and southern groups is not a result of a recent translocation, and instead these populations represent independent evolutionarily significant units. We conclude that these newly discovered and phenotypically unique cichlid populations are already threatened by hybridization with an invasive species, and propose that these irreplaceable genetic resources would benefit from conservation interventions.

The taxonomic diversity of the cichlid fish fauna of ancient Lake Tanganyika, East Africa

Ancient Lake Tanganyika in East Africa houses the world's ecologically and morphologically most diverse assemblage of cichlid fishes, and the third most species-rich after lakes Malawi and Victoria. Despite long-lasting scientific interest in the cichlid species flocks of the East African Great Lakes, for example in the context of adaptive radiation and explosive diversification, their taxonomy and systematics are only partially explored; and many cichlid species still await their formal description. Here, we provide a current inventory of the cichlid fish fauna of Lake Tanganyika, providing a complete list of all valid 208 Tanganyikan cichlid species, and discuss the taxonomic status of more than 50 undescribed taxa on the basis of the available literature as well as our own observations and collections around the lake. This leads us to conclude that there are at least 241 cichlid species present in Lake Tanganyika, all but two are endemic to the basin. We finally summarize some of the major taxonomic challenges regarding Lake Tanganyika's cichlid fauna. The taxonomic inventory of the cichlid fauna of Lake Tanganyika presented here will facilitate future research on the taxonomy and systematics and the ecology and evolution of the species flock, as well as its conservation.

Ecomorphological diversification of some barbs and carps (Cyprininae, Cyprinidae) in the Lower Mekong Basin of Thailand

Morphological variation is fundamentally related to various aspects of fish ecology, including foraging, locomotion, and habitat utilisation. Twenty-six species of closely related cyprinid fish (n = 502) were analysed for patterns of morphological variations by using geometric morphometric methods. Ecological data of feeding and habitat preferences were determined by the observations in fields and laboratory together with the gathering of bibliographic information. The findings of major variation displayed in all parts of the fish body and correlated with ecological parameters. Variations of head shape especially form and position of mouthpart involved with feeding behaviours, whereas the variations of body depth and length which affected swimming patterns reflected responsiveness of water currents and habitat uses. Adaptation of head shape and body elongation was remarkably related to the feeding regime, swimming manoeuvrability and habitat utilisation of the species. Some convergent variation was observed between the tribes Smiliogastrini and Poropuntiini. Therefore, we propose that the morphological diversity of cyprinine fish is mainly affected by ecological gradients, while phylogenetic effects on morphology are minor.

A functional trade-off between trophic adaptation and parental care predicts sexual dimorphism in cichlid fish

Although sexual dimorphism is widespread in nature, its evolutionary causes often remain elusive. Here we report a case where a sex-specific conflicting functional demand related to parental care, but not to sexual selection, explains sexual dimorphism in a primarily trophic structure, the gill rakers of cichlid fishes. More specifically, we examined gill raker length in a representative set of cichlid fish species from Lake Tanganyika featuring three different parental care strategies: (i) uni-parental mouthbrooding, whereby only one parental sex incubates the eggs in the buccal cavity; (ii) bi-parental mouthbrooding, whereby both parents participate in mouthbrooding; and (iii) nest guarding without any mouthbrooding involved. As predicted from these different parental care strategies, we find sexual dimorphism in gill raker length to be present only in uni-parental mouthbrooders, but not in bi-parental mouthbrooders nor in nest guarders. Moreover, variation in the extent of sexual dimorphism among uni-parental mouthbrooders appears to be related to trophic ecology. Overall, we present a previously unrecognized scenario for the evolution of sexual dimorphism that is not related to sexual selection or initial niche divergence between sexes. Instead, sexual dimorphism in gill raker length in uni-parental mouthbrooding cichlid fish appears to be the consequence of a sex-specific functional trade-off between a trophic function present in both sexes and a reproductive function present only in the brooding sex.

Dissecting a potential spandrel of adaptive radiation: Body depth and pectoral fin ecomorphology coevolve in Lake Malawi cichlid fishes

The evolution of body shape reflects both the ecological factors structuring organismal diversity as well as an organism's underlying anatomy. For instance, body depth in fishes is thought to determine their susceptibility to predators, attractiveness to mates, as well as swimming performance. However, the internal anatomy influencing diversification of body depth has not been extensively examined, and changes in body depth could arise as a by-product of functional changes in other anatomical structures. Using an improved phylogenetic hypothesis for a diverse set of Lake Malawi cichlid fishes, we tested the evolutionary association between body depth and the height of the pectoral girdle. To refine the functional importance of the observed substantial correlation, we also tested the coevolution of pectoral girdle height and pectoral fin area. The extensive coevolution of these traits suggests body depth in fishes like the Lake Malawi cichlids could diverge simply as a by-product of being tightly linked to ecomorphological divergence in other functional morphological structures like the pectoral fins.

Study of morphological variation of northern Neotropical Ariidae reveals conservatism despite macrohabitat transitions

BACKGROUND

Morphological convergence triggered by trophic adaptations is a common pattern in adaptive radiations. The study of shape variation in an evolutionary context is usually restricted to well-studied fish models. We take advantage of the recently revised systematics of New World Ariidae and investigate skull shape evolution in six genera of northern Neotropical Ariidae. They constitute a lineage that diversified in the marine habitat but repeatedly adapted to freshwater habitats. 3D geometric morphometrics was applied for the first time in catfish skulls and phylogenetically informed statistical analyses were performed to test for the impact of habitat on skull diversification after habitat transition in this lineage.

RESULTS

We found that skull shape is conserved throughout phylogeny. A morphospace analysis revealed that freshwater and marine species occupy extreme ends of the first principal component axis and that they exhibit similar Procrustes variances. Yet freshwater species occupy the smallest shape space compared to marine and brackish species (based on partial disparity), and marine and freshwater species have the largest Procrustes distance to each other. We observed a single case of shape convergence as derived from 'C-metrics', which cannot be explained by the occupation of the same habitat.

CONCLUSIONS

Although Ariidae occupy such a broad spectrum of different habitats from sea to freshwater, the morphospace analysis and analyses of shape and co-variation with habitat in a phylogenetic context shows that conservatism dominates skull shape evolution among ariid genera.